<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<style>
    *{
        margin: 0;
        padding: 0;
    }
    .nav{
        list-style: none;
        width: 300px;
        margin: 100px auto;
    }
    .nav > li{
        border: 1px solid #000;
        line-height: 35px;
        border-bottom: none;
        text-indent: 2px;
        position: relative;
    }
    .nav li:last-child{
        border-bottom:  1px solid #000;
        border-bottom-left-radius: 10px;
        border-bottom-right-radius: 10px;
    }
    .nav li:first-child{
        border-top-left-radius: 10px;
        border-top-right-radius: 10px;
    }
    .nav >li > span{
        display: inline-block;
        background-image: url(./img/right.png) ;
        width: 32px;
        height:32px ;
        position: absolute;
        right: 10px;
        top: 5px;

    }
    .sub >li{
        list-style: none;
        background-color: purple;
        border-bottom: 1px solid white;
    }
    .sub >li:hover{
        background: red;
    }

    .nav > .current >span{
        transform: rotate(90deg);
    }
    .sub{
        display: none;
    }
</style>
<body>
    <ul class="nav">
        <li class="">一级菜单<span></span>
            <ul class="sub">
                <li>二级菜单</li>
                <li>二级菜单</li>
                <li>二级菜单</li>
                <li>二级菜单</li>
                <li>二级菜单</li>
            </ul>
        </li>
        <li>一级菜单<span></span>
            <ul class="sub">
                <li>二级菜单</li>
                <li>二级菜单</li>
                <li>二级菜单</li>
                <li>二级菜单</li>
                <li>二级菜单</li>
            </ul>
        </li>
        <li>一级菜单<span></span>
            <ul class="sub">
                <li>二级菜单</li>
                <li>二级菜单</li>
                <li>二级菜单</li>
                <li>二级菜单</li>
                <li>二级菜单</li>
            </ul></li>
        <li>一级菜单<span></span>
            <ul class="sub">
                <li>二级菜单</li>
                <li>二级菜单</li>
                <li>二级菜单</li>
                <li>二级菜单</li>
                <li>二级菜单</li>
            </ul></li>
        <li>一级菜单<span></span>
            <ul class="sub">
                <li>二级菜单</li>
                <li>二级菜单</li>
                <li>二级菜单</li>
                <li>二级菜单</li>
                <li>二级菜单</li>
            </ul></li>
        <li>一级菜单<span></span>
            <ul class="sub">
                <li>二级菜单</li>
                <li>二级菜单</li>
                <li>二级菜单</li>
                <li>二级菜单</li>
                <li>二级菜单</li>
            </ul></li>
    </ul>
</body>
<script src="https://upcdn.b0.upaiyun.com/libs/jquery/jquery-2.0.2.min.js"></script>
<script>
    $(function () {
        //1.监听一级菜单的点击事件
        $(".nav > li").click(function () {
            //1.1拿到二级菜单
            var $sub =$(this).children(".sub")
            //1.2让二级菜单展开
            $sub.slideDown(1000);

            //1.3拿到所以非当前二级菜单
            var $otherSub =$(this).siblings().children(".sub")

            //1.4让所以非当前二级菜单收起
            $otherSub.slideUp(1000)

            //1.5让被点击的一级菜单箭头旋转
            $(this).addClass("current");

           //1.6让非被点击的一级菜单还原
            $(this).siblings().removeClass("current");

        })
        
    })

</script>
</html>